dbaflyer

dbaflyer

Well Known Member
I am starting to leak test the left tank and I'm apprehensive about putting too much air into the tank. I don't want to split it open after all that hard work. It seems like I can pump and pump my bicycle pump and the balloon size does not change. I don't believe there is a major leak anywhere as the balloon size you see is not changing. Am I just to cautious about too much air? And am I more likely to detect a leak if the air pressure inside is enough to force the air out through small holes/gaps?
LeftTankLeakTest4.jpg
 
use soapy water to check for small leaks

I would suggest spraying the tank with soapy water (if you haven't already) and then pump in the air to ensure that there are no leaks. When I did my first leak test, the balloon only inflated like in your picture, but I found several small leaks along the baffle. Once the leaks were fixed, it still seemed like it took a lot of pumping, but the balloon suddenly started to inflate to full size.
 
Stretch the balloon!

I just went through this with my left tank 2 weeks ago. Fun time with ProSeal.

Make sure you stretch the balloon out and blow it up a couple times before installing it on the vent. This will loosen the baloon up and not require such a huge force to blow it up more with your bike pump.

Lessons learned from my repair was to put some painters tape over the fuel cap to ensure there is no way for air to escape there, also wrap the balloon end with some tape where it is attached to the vent to ensure an air tight fitting. I just put the balloon on with a zip tie at first and had the same problem you are having, covered the gas cap and taped the balloon and it inflated perfectly and was the same size 24hr later!

2 weeks, 10 hours flying and no leaks yet!!!!! (Knocking on wood as we speak!)

Dan
 
Remember, the tank holds a *lot* of air; it will take a while to raise the pressure significantly with a hand pump.

The balloon will change size if air temp changes a lot over time.

You can rig up a water manometer & it will directly indicate your pressure rise in inches of water (I think that Van supplies a procedure that tells you how many inches of rise to use in testing, or you can convert 1 1/2 -2 psi to "water.)

As already mentioned, a very small leak will bleed down pressure about as fast as you can pump with a hand pump.

Charlie
 
esjacoby77 said:
......seemed like it took a lot of pumping, but the balloon suddenly started to inflate to full size.
Click to expand...
Exactly as you described, I find that at some point in the pumping process, the small balloon finally seems to yield to the pressure and quickly inflates to full size. Hearing the fuel tank creak as air pressure is increased can be a disconcerting sound but I reasoned the balloon would pop way before the tank would split. Has anyone (unfortunately) proved my theory wrong?

52av4x.jpg
 
the balloon came to life

Pumping no more air in the tank. I guess the balloon finally gave way and was pushed over the edge after a couple hours. I did blow up and stretch this balloon several times before using it. Thanks all for the advice.

LeftTankLeakTest5.jpg
 
It took me approximately 20 pumps from a full size bicycle pump to get 1 PSI in the tank (the amount recommended by Vans).
 
As noted above, the volume of air can change as a function of temperature. Also, many balloons will allow air to diffuse out over time (even overnight). I recommend the manometer test as it's more accurate.

greg
 
Rick6a said:
Exactly as you described, I find that at some point in the pumping process, the small balloon finally seems to yield to the pressure and quickly inflates to full size. Hearing the fuel tank creak as air pressure is increased can be a disconcerting sound but I reasoned the balloon would pop way before the tank would split. Has anyone (unfortunately) proved my theory wrong?

52av4x.jpg
Click to expand...

Rick,
I don't have an answer to your question but that is hands down the most beautiful proseal job I have ever seen. You sir, are the Rembrandt of Proseal!
 
aarvig said:
Rick,
I don't have an answer to your question but that is hands down the most beautiful proseal job I have ever seen. You sir, are the Rembrandt of Proseal!
Click to expand...

Notice also the stategic removal of the blue plastic, only around the rivets.

I also saw the proseal and thought wow, it must be fully sealed, the balloon is inflated, I was also amazed.
 
Baffle leak

What did you do to fix the leak? I am having exactly the same issue.

esjacoby77 said:
I would suggest spraying the tank with soapy water (if you haven't already) and then pump in the air to ensure that there are no leaks. When I did my first leak test, the balloon only inflated like in your picture, but I found several small leaks along the baffle. Once the leaks were fixed, it still seemed like it took a lot of pumping, but the balloon suddenly started to inflate to full size.
Click to expand...
 
cut some big holes in the baffle

Dave Taylor said:
What did you do to fix the leak? I am having exactly the same issue.
Click to expand...
The posts on my build log that detail the repair start here:
http://rv-7construction.com/2010/12/21/started-right-fuel-tank-repair-122110/

Basically, I cut 3" holes in the baffle for every bay that had a leak. I then resealed the tank skin/baffle joint with pro-seal by reaching in through the new holes (be generous with the sealant). Finally, I re-covered/sealed the new holes in the baffle using some 4" aluminum circles and closed-end blind rivets. Give it a week or more to dry, then re-test the tank.

A few others have detailed this repair on the forums as well. Once you get over the fear of cutting big holes in your baffle, the repair is relatively easy to do.

Good luck!
 
Did you pressurize the tank before submerging it? If not, I don't see how it would work. In fact, wouldn't water actually seep into the tank if there was a leak.
 
Balloon filled right away

I used my air compressor to pressurize my tank and the balloon filled immediately. The tank held pressure for 18 hrs before I ended the experiment. I suspect there are leaks in your tank. Spray with soapy water as others have suggested and look for bubbles. Also - remember to tape over the fuel cap.

4ddd70bf.jpg
 
Bicycle Pump

I used a bicycle tyre pump. It didn't take long and there was no danger of accidentally over pressurising.

Jim Sharkey
RV-6
 
why not use fuel?

After all it is a fuel tank and you don't have to fill it all the way up. I poured about a gallon into the tanks and stood them on end for a couple of days and then set it leading edge up for a while. Put them in the construction cradle leading edge down. Left them in the garage. Right next to the gas can for the lawnmower.
 
Someone already mentioned taping the fuel caps. I put the fuel caps inside a glove and then locked them in the openings.

Also, I found using a water manometer to be much easier than the balloon. The balloon will contract and expand with temperature changes, which you have to account for.

With the water column, you mark the water level when you start the test, and note the ambient temperature. You then wait until the next day, when the temperature is the same as when you started the test, and check that the water level is at the mark you drew the day before. If you are lucky, you can come back on day #3 and smile as the water is again at the same level :)

Here are some (mediocre) pictures:

http://rv7a.fabs-designs.com/2009/09/06/leak-testing-the-tanks/

Good luck!

Luis
 
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